What is the difference between mi5 and mi6?

It gets a little more complicated in that MI6 has its own "counter-intelligence" section. "MI5/MI6" were the original designations when both organisations came under the War Office, now the MOD - "MI" stands for military intelligence. read more

The binary distinction between MI5 and MI6 presented in some of the answers above is incorrect. As displayed on the MI6>FAQs and on the MI5 website>about us>myths sections, "SIS (MI6) collects secret intelligence overseas on behalf of the British Government. read more

Differences between the two organizations extend beyond focus. They are answerable to different people. The Mi5 answers to the Home Secretary. This is an indirect confirmation of the organization's focus on domestic as well as external threats. In contrast, the Mi6 answers to the Foreign Secretary in part due to its exclusive focus on external threats. read more

MI5 is internal/domestic, MI6 is external/foreign. That’s the gist of it. MI5 answers to the Home Secretary, while MI6 answers to the Foreign Secretary. They have roughly the same number of employees (a few thousand each, on paper anyway). read more